Manufacturing Engineering Multiple Choice Questions on “Crystallography-1”.
1. Which of the following has a non-crystalline structure?
a) Iron
b) Quartz
c) Silica glass
d) Tungsten
Answer: c
Clarification: In general, metals exist in a crystalline form. Iron and Tungsten being metals takes up body centered cubic crystalline structure at room temperature. The ceramic compound–silica (SiO2), can exist either in a crystalline form or in a non-crystalline form (amorphous form). While quartz, tridymite and cristobalite are known as its crystalline forms which are being differentiated based on SiO4 tetrahedra linkage style, silica’s non-crystalline (amorphous) form is just called as the silica glass.
2. Which of the following has less crystallinity?
a) Iron
b) Nickel
c) High density polythene
d) Low density polythene
Answer: d
Clarification: It is clear that, iron and nickel being metals possesses a crystalline form, whereas high density polyethylene (HDPE) and low-density ethylene (LDPE) are a class of polymers. These both thermoplastics are semi-crystalline nature, out of which LDPE exhibits a crystallinity of about 50-60% and HDPE of about 90%. Some people may term HDPE as crystalline, but it is more appropriate to restrict it in the category of semi-crystalline class.
3. Which of the following is a characteristic of crystalline structure?
a) High density
b) Low density
c) Range of melting point
d) Short range of order
Answer: a
Clarification: A crystalline structure has very close packing of atoms thus giving rise to high density to material it possesses when compared to its non-crystalline form. For example, quartz being the crystalline form of silica has a density of about 2.65 gm/cm3, whereas its ally–non-crystalline form silica glass has a density of 2.20 gm/cm3. For reference, the other properties being differentiated between crystalline and non-crystalline forms are tabulated below.
| Differentiating Parameter | Structure | |
|---|---|---|
| Crystalline Structure | Non-Crystalline Structure | |
| Geometry | Well defined geometrical shape | Random shape |
| Melting point | Definite melting point | Rage of melting point |
| Density | High density when compared to non-crystalline structure due to strong primary atomic bonding. | Low density when compared to crystalline structure due to weak secondary atomic bonding |
| Range of order | Long range of order (periodicity) | Short range of order (periodicity) |
| XRD Diffraction pattern | Sharp diffraction pattern | Broad hump |
| Examples | Iron, Steel, HDPE, Quartz, etc. | Metallic glass, silica glass, LDPE, etc. |
4. Which of the following is characteristic of non-crystalline structures?
a) Long range of periodicity
b) Well defined structure and geometry
c) Low density
d) Sharp diffraction pattern
Answer: c
Clarification: In non-crystalline structure, there is no definite packing of atoms, which makes them to possess any random shape, further these atoms are being bonded by weak secondary bonds with Van der Wall’s forces, thus giving a low density to material.
5. Which of the following factor is not responsible for the formation of a non-crystalline structure?
a) Atomic packing has open structure
b) Primary bonds are absent
c) Formation of 1-dimensional chain molecule
d) Strong secondary bond
Answer: d
Clarification: A non-crystalline structure is being formed by a secondary bonds or molecular bonds are formed as a result of weak Van der Wall’s of attractions which exist between various atoms. These intermolecular bonds can be further classified as dispersion bonds, dipole bonds, hydrogen bonds, which are all should be considered as weak secondary bonds.
6. Which of the following axis system is being satisfied by cubic crystal system?
a) a = b = c, α = β = γ = 90o
b) a ≠ b = c, α = β = γ = 90o
c) a = b ≠ c, α = β = γ = 90o
d) a = b = c, α ≠ β = ϒ = 90o
Answer: a
Clarification: Simple cubic have all sides equal and all angles equal. For reference, table of 7 Bravais lattices are tabulated below:
| S.No. | Crystal System | Conventional Unit Cell Axis System | |
|---|---|---|---|
| Lengths | Angles | ||
| 1 | Cubic | a = b = c | α = β = γ = 90o |
| 2 | Tetragonal | a = b ≠ c | α = β = γ = 90o |
| 3 | Orthorhombic | a ≠ b ≠ c | α = β = γ = 90o |
| 4 | Rhombohedral (Trigonal) | a = b = c | α = β = γ ≠ 90o |
| 5 | Hexagonal | a = b ≠ c | α = β = 90o, γ = 120o |
| 6 | Monoclinic | a ≠ b ≠ c | α = γ = 90o ≠ β |
| 7 | Triclinic | a ≠ b ≠ c | α ≠ β ≠ γ ≠ 90o |
*Note—Order trick: C-T-O-R-H-M-T (Decreasing symmetry)